(a) Technical Field
The present disclosure relates, generally, to an electric oil pump. More particularly, it relates to an apparatus and method for controlling the operation of an electric oil pump for creating a working fluid pressure in a transmission and a clutch for a hybrid vehicle.
(b) Background Art
Hybrid vehicles are the vehicles of the future that employ a motor as an auxiliary power source as well as a gasoline engine to provide a reduction in exhaust gas and an improvement in fuel efficiency. As shown in FIG. 1, a typical hybrid vehicle includes an engine 10 and a drive motor 30 as power sources for running the vehicle, an engine clutch 20 for connecting the engine 10 and the drive motor 30, an integrated-starter generator (ISG) 11, a high voltage battery 31, and an inverter 32, which are used for the operation of the engine 10 and the drive motor 30.
Further, a transmission 40 for transmitting power to a drive shaft 1 is suitably connected to an output of the drive motor 30, an electric oil pump (EOP) 71 and a mechanical oil pump (MOP) 75 are provided to supply working fluid pressure to the engine clutch 20 and the transmission 40, and an auxiliary battery 74 is preferably provided to supply driving power to the electric oil pump 71.
Although not shown in the figure, a hybrid control unit (HCU), a motor control unit (MCU), and a battery management system (BMS) are provided as control means for the components. Moreover, a transmission control unit (TCU) 61 for controlling the transmission 40 and an electric oil pump control unit (OPU) 62 for directly controlling the operation of the electric oil pump 71 are further provided.
Preferably, the hybrid vehicle with the above-described configuration is driven in an electric vehicle (EV) mode, which is a pure electric vehicle mode using only the power of the drive motor 30 which is suitably transmitted to the transmission 40, or in a hybrid electric vehicle (HEV) mode, which is an auxiliary mode using both the power of the engine 10 as a main power source and the power of the drive motor 30 as an auxiliary power source which are transmitted to the drive shaft 1 through the clutch 20 and the transmission 40.
In the hybrid vehicle, the electric oil pump 71 is driven by the power of the auxiliary battery 74 under the control of the TCU 61 and OPU 62 and the mechanical oil pump 75 is connected to a drive shaft of the drive motor 30 and is driven by the mechanical energy serve to produce a hydraulic pressure by supplying working fluid to control valves of the transmission 40 and the clutch 20 when a driver wishes to start his or her vehicle.
FIG. 2 shows the flow of automatic transmission fluid (ATF) used for the operation of the transmission and the clutch, in which the electric oil pump 71 and the mechanical oil pump 75 are driven to suitably supply the oil stored in an oil tank 51 to a valve body 53 through a hydraulic line 52.
Typically, the electric oil pump 71 supplies hydraulic pressure to the hydraulic line 52 in the EV mode, and the mechanical oil pump 75 supplies hydraulic pressure to the hydraulic line 52 together with the electric oil pump 71 in the HEV mode (in which the engine is driven and the engine clutch is connected).
Accordingly, FIG. 3 shows the drive modes of a typical electric oil pump. As shown in FIG. 3, the operation of the electric oil pump is suitably controlled in various drive modes according to the state of the vehicle. Preferably, the drive modes may be classified in to a high speed control mode as an initial operating condition, in which the pump is driven at high speed for a short period of time, such as several seconds, to ensure the hydraulic pressure response during start-up (IG, START ON), a low speed control mode, in which the pump is driven at low speed to minimize the power consumption under idle conditions when the vehicle is stopped (vehicle speed is 0 & brake is on, or gear lever is in N or P), a middle speed control mode as a normal operating condition, in which the pump is driven at middle speed when the vehicle is normally driven, and a non-control mode in which the operation of the pump is stopped (EOP is off/MOP is on).
Here, preferably, the high speed control mode is suitably performed to ensure the hydraulic pressure response by applying high hydraulic pressure to the hydraulic line with high pressure pumping force for a predetermined period of time, and the middle speed control mode is performed when the vehicle is normally driven.
Preferably, the entrance into the middle speed control mode and the non-control mode is suitably determined based on the rotational speed of the mechanical oil pump and the transmission input torque. In the non-control mode, the operation of the electric oil pump is suitably stopped, and thus only the mechanical oil pump supplies hydraulic pressure to the hydraulic line.
Further, in order to produce a line pressure required in the transmission and the clutch in the control of the operation of the electric oil pump, it is necessary to drive the pump at an optimal rotational speed. Typically, the pump is suitably controlled at a predetermined target rotational speed based on the temperature of the oil (ATF) in each drive mode.
Preferably, the TCU extracts a target rotational speed (RPM) according to the oil temperature from stored data for each drive mode and suitably transmits it to the OPU through a CAN communication. Then, the OPU controls the operation of the motor of the electric oil pump based on the target rotational speed transmitted from the TCU and, at the same time, feeds back the control result to the TCU.
FIG. 4 shows an example in which the rotational speed of the motor is controlled based on the oil temperature. Preferably, since the load torque varies according to the oil viscosity, the rotational speed of the motor is controlled based on the oil temperature which is significantly associated with the oil viscosity. Referring to FIG. 4, for example, the higher the oil temperature, the more the oil viscosity is reduced. Thus, if the oil viscosity is lower, the rotational speed of the motor of the pump is increased to form a pressure defined in the hydraulic line.
As such, the oil temperature reflecting the oil viscosity and measured by a temperature sensor is used as a control variable. Although it is necessary to control the driving speed based on an accurate actual viscosity value of fluid in the control of the operation of the pump, the measurement value of the temperature sensor is used to control the operation of the pump in a typical vehicle.
However, the viscosity characteristics of the oil are changed as the use of the transmission continues, which are different from those of a new product, and thus it is impossible to accurately predict the actual load torque.
Preferably, in the case where the oil temperature is measured to reflect the oil viscosity during the control of the rotational speed of the motor in the conventional manner, a temperature-rotational speed map reflecting the initial conditions of new oil is used as it is, and thus after the elapse of a predetermined time, it can be difficult to accurately reflect the actual state of the oil to control the operation of the pump.
Accordingly, there remains a need in the art for apparatus and methods for controlling the operation of an electric oil pump.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.